Sensor connection interfaces, currently called “current limiter terminations” (CLTs), are interposed between sensors delivering a two-state electric response and the analog inputs of an electronic circuit. The function of such interfaces is to size the signals delivered by the sensor to make them compatible with the levels acceptable by the electronic circuit.
A first family of sensors involves so-called “two-wire” sensors, where the sensor power supply transits through the output of the sensor, and thus through the interface between the sensor and the microcontroller. According to the state of the detection or measurement element of the sensor, said sensor delivers a high or low state, that is, it connects or not the power supply terminal to the output terminal of the sensor.
A second family relates to so-called three-wire sensors where the sensor power supply is separated from the output signal.
The sensor supply voltage is often different from that of the microcontroller. Therefore, the interface circuit is used to limit the current and to provide a signal acceptable to the microcontroller inputs.
However, the difference between power supply voltages generates a strong dissipation in interface circuits, especially for two-wire sensors. This dissipation may reach several watts for circuits intended to process many inputs.
Such a high dissipation currently limits the number of inputs of a same interface circuit. It would be desirable to have interface circuits with a greater number of inputs.
It would further be desirable to decrease the dissipation of the interface circuit.